1. Field of the Invention
The invention relates to a stabilizing device for extending the characteristic diagram of a compressor.
2. Discussion of Background
It is known that during the rotation of a compressor impeller, a gap flow appears in the gap between the rotating outer edges of the impeller vanes and the stationary casing, this flow taking place from the side of the vane at high pressure to that at low pressure. Together with other flow phenomena in the inlet part of the centrifugal impeller, this gap flow can lead to a vortex. Due to this vortex, the efficiency of the compressor is reduced and the stable range of the compressor characteristic becomes narrower.
When turbo-compressors are used, an attempt is made to achieve a steadily falling characteristic, without hysteresis, as the flow increases in order to achieve a high level of reliability during part-load operation. Such continuous characteristics are described as being stable. As the pressure ratio at the design point is increased, however, stable characteristics become more difficult to achieve at part load. For this reason, attempts are made to generate the desired stable characteristics by means of additional stabilizing devices.
The stabilizing device described, for example, in the Patent Specification CH 675 279 consists of a recess in the casing of a centrifugal compressor, a stabilizing ring being integrated in this recess. The recess and the stabilizing ring are arranged in front of the impeller and outside the main flow. Stabilizing vanes are present at the outer periphery of the stabilizing ring and these are anchored on the inner contour of the recess. The disadvantage of this solution consists in the complicated design of the casing, the ring and the stabilizing vanes. In addition, the vibration loading of the impeller vanes in the inlet region, which is large in any case, is further increased by the stabilizing appliance.
A stabilizing device is known to the applicant in which the disadvantages just mentioned are reduced. This device consists of a ring permanently connected to the impeller vanes, a relatively large radial recirculation passage being arranged between the ring and the casing of the compressor. When the compressor is strongly throttled, a recirculation flow is made possible there and this contributes to stabilizing the characteristic diagram. The ring supports the vane inlet edges in both the radial and tangential directions and, by this means, reduces the vane vibrations. The disadvantage of this solution consists in the necessity for a relatively large recirculation passage and the fact that for many centrifugal compressors, the recirculation is undesirably strong.